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Investigation of Preparation and Absorbing Properties of Rare Earth Elements Doped BaTiO₃ and BaFe₁₂O₁₉

Author: LiuYanKun
Tutor: FengYuJie
School: Harbin Institute of Technology
Course: Environmental Engineering
Keywords: Rare earths Doping Barium titanate Ferrite Absorbing properties
CLC:
Type: PhD thesis
Year: 2008
Downloads: 820
Quote: 1
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Abstract

With the rapid development of modern microwave electronics technology with modern radar and electromagnetic radiation impact on the environment is increasing, after following the noise pollution, air pollution, water pollution, electromagnetic pollution has become a threat to the survival of mankind, the fourth largest public nuisance, electromagnetic radiation protection has increasingly attracted attention. For the day-to-day electromagnetic pollution protection requirements, design and preparation of absorbing material is an effective way to solve electromagnetic pollution hazards. Therefore, the study of the electromagnetic wave absorption material has a very important meaning, preparation of performance absorbing materials become the research focus. The barium titanate is an electrical loss material, ferrite is a magnetic loss material, which belong to two distinct types of electromagnetic radiation protection material, and can be used doping treatment to adjust the absorbing band of the absorbents. But the absorption intensity, the bandwidth can not meet the requirements of the new absorbing materials. Excellent microwave absorbing properties of rare earth elements, the right amount of doping is expected to improve the absorbing properties. This article focuses on rare earth doped barium titanate and ferrite materials structure and impact absorbing performance. Barium acetate, tetrabutyl titanate as raw material, the sol - gel prepared nano barium titanate powder. Optimize and determine prepared barium titanate optimum conditions, namely: sol concentration 0.5mol / L, the amount of glacial acetic acid 400ml/mol precursor, water bath temperature of 60 ℃, gel calcination temperature of 850 ° C. With XRD, Raman, FT-IR, SEM, TG-DTA, vector network analyzer test analysis method, the crystal structure of barium titanate material, surface morphology, gel thermal decomposition process and absorbing performance. The results show that: the obtained barium titanate particles have a mean particle size of 63nm, a pure tetragonal phase crystal phase, and in the 2 ^{1 the 8GHz frequency band the reflection loss is less than-10dB of the absorption band of 1.9GHz minimum reflection loss peaks in 4.4GHz, peak-25dB, has better electromagnetic absorption performance. Barium titanate sol-gel process has been optimized for the preparation of rare earth lanthanum (La), cerium (Ce), neodymium (Nd), europium (Eu), gadolinium (Gd), dysprosium (Dy) doped barium titanate nano materials. Investigated rare earth type of barium titanate crystal structure, lattice constant, particle size, surface morphology and microwave absorbing characteristics. : To The all rare-earth-doped samples the formation of tetragonal barium titanate microcrystalline well developed grain, particle size between 30 ^{6 0nm. The rare earth doping causes the lattice distortion, so that the lattice constant a larger particle refinement of the crystal axis ratio becomes smaller, the cell volume shrinkage. Electromagnetic performance parameters have taken place in the blue shift of the pressure peak reflectivity decreases absorption bands broaden absorbing properties has been significantly improved. Among them, Nd, La, Ce doped greater impact, the minimum reflectance of the barium titanate samples, the minimum reflectivity is less than-50dB; Nd, Eu contribute to broaden the band width, a band width of less than-10dB broaden 2 times more, Ce contribution to broaden the bandwidth minimum, an increase of only 0.5GHz. La doping the barium titanate material reflection loss peak to the amplitude of the high-frequency mobile. Example, the rare earth lanthanum rare earth doped amount for the structure and properties of barium titanate lattice constant a decreases gradually with increasing La content, grain size, crystal axis ratio and unit cell volume are increased and then decreased. The doping amount was 0.2%, 0.6% of rare earth effectively reduce minimum reflectance of the barium titanate material, broadening the absorption band. This selection of the sol-gel self-propagating prepared by the M-type barium ferrite of BaFe ₁₂ O ₁₉. Analysis of the citric acid, pH value of the material magnetic energy influence of angle from the magnetic energy, results showed that: citrate ratio of the level of the saturation magnetization (Ms) had no significant effect on the coercive force (Hc) have a significant impact, with the increase of the amount of citrate, the diameter gradually decreases, and the coercive force is gradually increased. With sol pH value rises, the magnetic powder Ms was increased and then decreased trend in pH = 7.00 point up to the maximum, the coercivity with the sol pH changes are not showing a significant change. According to the agglomeration mechanism, analysis of citric acid, pH value, polyethylene glycol is the control agglomeration contribution. Finalize the sol-gel conditions since spread prepared by M-type barium ferrite ratio of 2:1 for the citric acid with metal ions, the pH value of 7.0, polyethylene glycol 20g / L. With TG-DTA, XRD analysis to determine the M-type barium ferrite calcination temperature of 850 ° C, the the calcined time of 3h. Under these conditions, the preparation of barium ferrite materials through analysis Hexagonal M-type ferrite, the the smallest reflectance of-12dB, less than-10dB absorption band width is only 0.6GHz, poor absorbing properties. Using optimized barium ferrite sol-gel self-propagating process, preparation of Ce, Dy doped barium ferrite materials. Examine rare earth doped barium ferrite material structure, magnetic properties and microwave absorbing properties. The results show that: the sample formation of the various doping amount of the M-type ferrite the MS almost unchanged with the increase in the amount of the rare earth doping, but under the same conditions than the undoped ferrite of BaFe ₁₂ O ₁₉ Ms decreased; coercivity Hc with increasing doping x first decreases and then increases to a minimum value at x = 0.2. 2 ~ 18GHz range, rare-earth doped makes BaFe ₁₂ O ₁₉ reflectivity of the material is significantly reduced effectively broadening of BaFe ₁₂ O < materials bandwidth sub> 19 , Ce doped than the Dy doping. Shows that the rare-earth-doped effective improvement of barium titanate, ferrite material absorbing performance.}}

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